1. Field of the Invention:
This invention relates to an apparatus for shaping synthetic resin material of a type, in which a thermoplastic synthetic resin sheet is continuously shaped into a desired form, while it is being drawn by suction onto the surface of a shaping drum, and then subjected, depending on necessity, to any required processing.
2. Prior Art
An apparatus for shaping a thermoplastic synthetic resin sheet into a desired form, while it is being continuously drawn by suction onto the surface of a cylindrical shaping drum, has been known in U.S. Pat. No. 3,314,110. The shaping apparatus as taught in this patent is such that a heated sheet of a synthetic resin material is caused to contact on the surface of a cylindrical shaping drum, and then this synthetic resin sheet is drawn by suction onto the surface of this shaping drum by means of a plurality of tiny holes communicatively connected to a vacuum tank provided in the drum, thereby continuously shaping the synthetic resin sheet into a desired form. This shaping apparatus, however, possesses such defect that, although the shaping is primarily carried out by the suction drawing of the heated synthetic resin sheet around the shaping drum, if the surface temperature of the shaping drum is low, the synthetic resin sheet becomes immediately hardened upon its contact with the surface of the shaping drum with the consequence that no sufficient shaping operation can be accomplished. No sufficient shaping is possibly achieved by this apparatus unless approximately two hours is taken from commencement of the shaping operation. On the other hand, as the shaping operations are repeatedly performed with this apparatus, the temperature of the shaping surface of the drum rises due to heat of the heated synthetic resin sheet material accompanying sticking of the synthetic resin sheet, which has completed the shaping, onto the surface of the shaping drum with utter difficulty in peeling the sheet off the shaping surface of the drum. In order therefore to prevent the shaping drum of this apparatus from its undesirable rise in the surface temperature, an air blower is provided at one side portion of the shaping drum, through which the cooling air is blown onto the shaping surface of the drum to reduce the temperature, as has heretofore been practiced. However, in the case of cooling the shaping surface by the external air, not only adjustment of the shaping drum to an appropriate temperature in accordance with the material used is impossible, but also maintenance of the surface temperature of the shaping drum at a constant level against variations in the ambient temperature and increase in the production quantity cannot be performed properly.
Such shaping apparatus has been improved further by the present inventors as taught in the U.S. Pat. No. 3,837,973, although the problem of the temperature control in this apparatus still remains to be unsolved.